1. Technical Field
The present technology relates to a pneumatic radial tire for use on passenger cars, and particularly relates to a pneumatic radial tire for use on passenger cars by which steering stability when high-speed running can be enhanced and flat spot resistance performance can be improved.
2. Related Art
Generally, pneumatic radial tires for use on passenger cars have a structure in which a carcass layer, including a plurality of carcass cords oriented in a tire radial direction, is mounted between a pair of bead portions; a belt layer is disposed on an outer circumferential side of the carcass layer in a tread portion; and, furthermore, a belt cover layer is disposed on an outer circumferential side of the belt layer.
Conventionally, various organic fiber cords have been used as reinforcing cords of the belt cover layer. Particularly, nylon fiber cords have been widely used (e.g. see Japanese Unexamined Patent Application Publication No. H06-024208A). However, creep set strain of nylon fiber cords is great and, therefore, there is a problem that flat spots are prone to occur in pneumatic tires using such cords for the belt reinforcing layer.
Thus, consideration has been given to using steel cords in place of nylon fiber cords. However, there is a problem in that simply replacing nylon fiber cords with steel cords results in an excessive increase in rigidity of the belt cover layer, which leads to a decline in steering stability.